The present invention relates to a radiation image detecting apparatus having its radiation image receiving plane composed of a two-dimensional array of unit radiation sensors and having its image signal processing electronic circuits integrated in groups.
As a typical example of radiation image detecting apparatus, an X-ray camera using an emulsion film is well known. One of the disadvantages of such an apparatus using a film is that it takes a long time to finally provide a picture (photograph) of an image projected on the emulsion film, owing to the film development process. Another disadvantage is that limited linearity of darkness level of the emulsion makes it impossible to provide a high quality picture precisely reflecting the radiation intensity variations on an image projected on the emulsion film. Moreover, in case of an X-ray camera for use in diagnosis, a dose of X-rays to be irradiated to a human body is relatively large.
To overcome the above mentioned disadvantages, in case of detecting an X-ray image, there has been developed an apparatus in which emulsion film is replaced with a combined system of an X-ray image intensifier and a TV camera. According to this apparatus, an X-ray image projected on the X-ray image intensifier is converted to an electrical picture signal by the TV camera and then displayed on a CRT screen. However, this type of X-ray image detecting system also has a disadvantage: the dynamic range of the TV camera is smaller than that of a general radiation image to be detected, resulting in the quality deterioration of the picture obtained.
Another possible alternative method of radiation image detection is by means of a G-M counter. According to this method a radiation image is converted to an electrical picture signal by a G-M counter scanning mechanically on the plane where a radiation image is formed. The method by a G-M counter is suitable for analyzing local details of the image precisely, but inconvenient for picturing the entire aspect of the image, and therefore it often applies to an X-ray analysis of crystal rather than an X-ray image detection.
In addition, the apparatus using an emulsion film and that using a G-M counter have a common disadvantage that they are not suitable for the detection of an image whose profile or intensity distribution varies rapidly, because of an emulsion film exposure time or a G-M counter scanning period.
Such a disadvantage can be overcome by constituting the radiation image receiving plane with a numerous number of picture elements made of unit radiation sensors. All the picture element signals coincidentally outputted from the picture elements are once stored in a memory and then displayed on a CRT screen to give the entire picture of an image projected on the radiation image receiving plane at an instance. Though the method based on this principle has already been applied to a .gamma.-ray image detecting apparatus, many problems are still left unsolved in realizing a highly sensitive and resolving apparatus. In case of an X-ray image detecting apparatus, for example, for use in diagnosis, the image detection is necessarily completed within several milliseconds with a sensitivity capable of detecting one X-ray photon, covering an image receiving area of 30 cm.times.30 cm constituted with about 1000.times.1000 unit picture elements. Such requirements can be fulfilled, in principle, by constituting the radiation (X-ray) image receiving plane with an X-ray scintillator board accompanied by an array of light signal processing IC packages disposed with their light signal input windows directed and closely contacted to the rear surface of the scintillator board, the windows each having an array of photoelectric sensors each of which constitutes the signal input stage of each of the circuits integrated in the respective IC packages. An X-ray image projected on the scintillator board and converted to a visible-light image by the same is detected through the arrayed photoelectric sensors with the image divided into picture elements. However, the signal input window of the light signal processing IC now available has an area of only about one square centimeter wherein about 32.times.32 photoelectric sensors are included at most. Therefore, not only the scintillator board having an area of 30 cm.times. 30 cm must of course be accompanied by a large number of ICs, but also the clearances formed around the signal input windows of the ICs form a large-areal check-patterned dead space on the area of the image to be detected and make the apparatus impractical.